1.(a) F*T* = change in momentum
(b) *F*t = change in momentum: Remember that, (a) and (b), for an object brought t rest, the impulse is the same, no matter how it is stopped. But, if the time is short, the force will be large.

2.*Ft = ∆(mv)*: This relationship is derived by rearranging Newton's second law to make the time factor more evident. If we equate the formula for acceleration, a =F/m, with what acceleration actually is, a = ∆v/∆t, we get F/m = ∆v/∆t. From this we derive F∆t = ∆(mv). Calling ∆t simply t, the time interval, Ft = ∆(mv).

3.By momentum we mean...: Inertia in motion.

4.Case 1: Increasing Momentum: To increase the momentum of an object, it makes sense to apply the greatest force possible for as long as possible. The forces involved in impulses usually vary from instant to instant. When we speak of forces in this chapter, we mean the average force.

5.Case 2: Decreasing Momentum: It takes the same impulse to decrease your momentum to zero. The same impulse does not mean the same amount of force or the same amount of time; rather it means the same product of force and time. By hitting a haystack instead of a wall, you extend the time during which your momentum is brought to zero. A longer time interval reduces the force and decreases the resulting deceleration. For example, if the time interval is extended 100 times, the force is reduced to a hundredth. Whenever we wish the force to be small, we extend the time of contact. Hence, the padded dashboards and airbags in motor vehicles.

6.Case 3: Decreasing Momentum over a Short Time: (a) When a boxer moves away (rides with the punch), he extends the time and diminishes the force.
FT = change in momentum
(b) If the boxer moves into the glove, the time is reduced and he must withstand a greater force.Ft = change in momentum
In both cases, the impulse provided by the boxer's jaw reduces the momentum of the punch.

7.Elastic collision: A collision in which colliding objects rebound without lasting deformation or the generation of heat.

8.If the change in momentum occurs over a long time, the hitting force is small.: mV → FΤ

9.If the change in momentum occurs over a short time, the hitting force is large.: mV = Ft

10.If you wish to change the momentum of an object,: exert impulse on it. Only an impulse external to a system can change the momentum of the system. Internal forces and impulses won't work. For example, the molecular forces within a base have no effect on the momentum of the baseball (because the molecular forces are internal forces).

11.Impulse: The product of the force acting on an object and the time during which it acts.

12.Impulse =: change in momentum

13.In any collision, we can say:: Net momentum before collision = net momentum after collision.

14.Inelastic collision: A collision in which the colliding objects become distorted, generate heat, and possibly stick together.

15.Law of conservation of momentum: In the absence of an external force, the momentum of a system remains unchanged. Hence, the momentum before an event involving only internal forces is equal to the momentum after the event: *mv (before event) = mv (after event)

16.momenta: plural form of momentum

17.Momentum: The product of the mass of an object and its velocity.Momentum = mass × velocity

18.momentum (Glossary definition): Inertia in motion. The product of the mass and the velocity of an object (provided the speed is much less than the speed of light). Has magnitude and direction and therefore is a vector quantity. Also called linear momentum, and abbreviated p.p = mv

21.Momentum is conserved in collisions--: that is, the net momentum of a system of colliding objects is unchanged before, during, and after the collision. This is because the forces that act during the collision are internal forces--forces acting and reacting within the system itself. There is only a redistribution or sharing of whatever momentum exists before the collision.

22.Momentum is...: a property of moving things.

23.Momentum, like the quantities velocity and force,: has both direction and magnitude. It is a vector quantity. Like velocity and force, momentum can be cancelled.

24.Relationship of impulse and momentum: Impulse is equal to the change in momentum of the object that the impulse acts upon. In symbol notation, Ft = ∆mv